Container wall with rupturable weakening line

ABSTRACT

An improved method of forming and a construction for a digitally openable container closure. Included therein is a container wall having an inwardly displaceable opening panel defined by a fracturable web which has been formed by selectively displacing metal adjacent a predetermined line substantially perpendicular to the surface of the container wall and by extruding metal between substantially parallel die surfaces which are disposed at an angle to the plane of the container wall. Formed concurrently therewith is an integral inclined deflectable portion projecting outwardly from the container wall adjacent the fracturable web and which deflectable portion is adapted to effect, in response to digitally applied inwardly directed pressure, a relative displacement between the rim of the panel and the lip of the adjacent container wall to selectively strain the web and initiate fracture thereof to permit inward displacement of an opening panel of greater extent than the size of the opening formed in the container wall by the separation of said panel.

United States Patent 1191 Urmston Dec. 30, 1975 CONTAINER WALL WITHRUPTURABLE WEAKENING LINE Hugh C. Urmston, Richmond, Ind.

22 Filed: May 7,1973

21 Appl. No.: 357,937

Related U.S. Application Data [63] Continuation-in-part of Ser. No.281,541, Aug. 17,

[75] Inventor:

[52] U.S. Cl 220/268; 113/121 C; 215/253 [51] Int. Cl. B65D 17/00 [58]Field of Search 220/27, 48, 268, 266, 276; 113/121 C, 215/253 [56]References Cited UNITED STATES PATENTS 2,210,225 8/1940 Walensky 220/2663,221,924 12/1965 Harvey et a1. 220/271 3,227,304 l/l966 Asbury 220/483,292,826 12/1966 Abplanalp 270/89 A 3,362,569 l/1968 Geiger 220/273,362,570 l/l968 Geiger 220/27 3,638,825 2/1972 Franck et a1 220/273,730,381 5/1973 Franck et al..... 220/27 3,759,206 9/1973 Dalli et a1.220/27 3,779,417 12/1973 Klein 220/27 FOREIGN PATENTS OR APPLICATIONS400,823 8/1909 France 220/266 810,309 3/1937 France 220/268 422,05212/1934 United Kingdom.... 220/270 1,147,182 4/1969 United Kingdom....220/265, 1,964,091 12/1969 Germany 220/266 Primary Examiner-William 1.Price Assistant ExaminerAllan N. Shoap Attorney, Agent, or Firm-David W.Brownlee, Esq.

[57] ABSTRACT An improved method of forming and a construction for adigitally openable container closure. Included therein is a containerwall having an inwardly displaceable opening panel defined by afracturable web which has been formed by selectively displacing metaladjacent a predetermined line substantially perpendicular to the surfaceof the container wall and by extruding metal between substantiallyparallel die surfaces which are disposed at an angle to the plane of thecontainer wall. Formed concurrently therewith is an integral inclineddeflectable portion projecting outwardly from the container walladjacent the fracturable web and which deflectable portion is adapted toeffect, in response to digitally applied inwardly directed pressure, arelative displacement between the rim of the panel and the lip of theadjacent container wall to selectively strain the web and initiatefracture thereof to permit inward displacement of an opening panel ofgreater extent than the size of the opening formed in the container wallby the separation of said panel.

24 Claims, 10 Drawing Figures US. Patent Dec. 30, 1975 Sheet 3 of 4 \i m& 'I 4 4e F7619, W 22 Q U.S. Patent Dec. 30, 1975 Sheet4 of4 3,929,251

CONTAINER WALL WITH RUPTURABLE WEAKENING LINE This application is acontinuation-in-part of .my copending application Ser. No. 281,541,filed Aug. 17,

BACKGROUND OF THE INVENTION This invention relates to metal containerclosures and more particularly to an improved method and apparatus forforming and construction for a digitally openable container end closurethat not only exceeds the stringent and competitively dictated presentday commercial economic and performance criteria but also satisfies allecology based governmental regulations now extant.

The metal container industry and its ever increasing demands for thinsheet metal has been one of the major motivating factors in both thegrowth and strength of our domestic economy. At the present day, forexample, about 40 billion metal cans are fabricated each year alone tocontain, preserve and transport beverages, such as soda and beer. Overthe past 75 years or more, the ever increasing demands for productintegrity backed up by governmental regulations and juridical pressureshave, in an environment of continually increasing cost sensitivity,resulted in the development of commercially and competitively dictatedinterrelated economic and performance criteria of ever increasingstringency for metal containers. In the more recent years thecompetitive pressures attendant the fabrication of metal containers hasbeen further complicated by the changing habits of the consumer and amarked increase in the long standing desire for metal containers thatcould be manually opened at the point of consumption without employmentof auxiliary tools or the like. In the beverage field, such demand wasrecently satisfied, despite the existence of great numbers of suggestedexpedients therefor in the prior art and attendant unfavorable economicconsiderations, by the industry-wide fabrication of the Fraze type ofpull tab easy open end closure. The widespread utilization of such typeof end closures has, apart from the increased costs inherently attendantits fabrication due to increased metal content thereof and requiredmultiple fabricating operations, created a serious ecology problem dueto the hazards attendant the relatively sharp-edged removable tabportion thereof and the propensity of consumers to indiscriminatelydispose of such tabs immediately following their separation from thecontainer. In part, the problems attendant such indiscriminate tabdisposition have resulted in the actual or contemplated banning of suchclosures in certain jurisdictions with the concommitant creation ofproblems of major magnitude for the can fabricators.

As noted above, the prior art, and notably the patented art, is repletewith hundreds suggested expedients for achieving the long desiredobjective of simplified can opening, including many suggested expedientsfor can closures that can be digitally opened, i.e. manually openedwithout the use of auxiliary tools or the like. Included in suchexpedients were the use of container walls and end closures whichincluded weakening lines or score lines defining tear strips or panelswhich could either be depressed into or pried out of a container to formeither a vent or a pouring opening therein. Closures of this type areexemplarily disclosed in a number of U.S. Pat. Nos. including Newman1,805,003, fried 2,176,898, Asbury 3,227,304, Asbury 3,246,791, Asbury3,355,058, Klein et a1 3,334,775, Foss et al 3,410,436, Punte 2,187,433,Punte 2,289,452, Punte 2,312,358, Punte 2,312,359, Fink 2,119,533 andPunte 2,120,186. Such end closures have sometimes required the use ofrigid tools, such as a coin or a fork, to rupture the score line aroundthe removable panel in order to form an opening in the end closure.Several of such end closures have included embossments in the removableportion to facilitate opening of the removable portion by pressing orprying against embossments.

It has also been suggested to form a weakening line in the form of afracturable web in such a container closure by displacing metal alongone side of a line at right angles to the initially undisplaced surfaceof the container wall in such a way that the edge defining the peripheryof the removable wall portion underlaps the corresponding edge of thenon-removable wall portion and has an abrupt change in cross-sectionalwall thickness as is disclosed in Geiger U.S. Pat. No. 3,362,569. Thatpatent discloses that the removable wall portion in such a closure hasgreater resistance against severance of the fracturable web as would beoccasioned by internal pressure than'it has against severance due to anopening force applied against the exterior surface of the portion. Ithas been found, however, that displacing metal at right angles to thesurface of the sheet in the manner taught and disclosed in Geiger U.S.Pat. No. 3,362,569 can cause small cracks in, or accidental severanceof, the fracturable web that is formed, particularly in hard tempermetal. Punte U.S. Pat. No. 2,187,433 suggests another expedient whereina weak ened thinned portion is formed in a container wall by thinningthe wall between a rounded corner of a movable die member and a diesurface disposed at a 45 angle to the axis of displacement of themovable die member. Other expedients suggested by the art for theformation of particularly shaped weakened areas are embodied in U.S.Pat. Nos. to Barrath 540,625, Fraze 3,291,336, Cookson 3,434,623,Cookson 3,698,590 and Baumeyer et al 3,693,827.

Insofar as I am aware, none of these suggested expedients haveapparently been able to satisfy the stringent and complementallyinterrelated economic and performance criteria necessary for widespreaduse on beverage and like containers. As evidenced by the span of yearscovered by the above noted patents, it has long been desired to have acontainer end closure or container wall with a removable portion in itwhich can be inwardly displaced from the end closure or wall withoutneed for a separate tool or a pull tab attached to the removableportion. While the Fraze type of pull tab easy open end closure is, asnoted above, presently in wide use despite its additional expense, thecurrent ecology induced pressures make it desirable to utilize theconcepts of the Geiger patent, but to provide a method of forming afracturable web that is not subject or vulnerable to small cracks orfailure therein and which satisfies the current stringent andcomplementally interrelated economic and performance criteria necessaryfor widespread commercial use.

SUMMARY OF THE INVENTION This invention may be briefly described asincluding, in its broad aspects, the provision of an improved method andapparatus for forming and construction for a digitally openablecontainer end closure. In such broad aspect it includes a container wallhaving a particularly contoured fracturable web defining an inwardlydisplaceable opening panel having an upper surface on the rim thereofintersecting the inner marginal edge of the lip of an adjacentparticularly contoured deflectable portion in a first exposed corner andwith the undersurface of said lip disposed in substantial alignment withsaid upper surface of said panel rim and intersecting the outer marginaledge of said rim in a second corner. The deflectable portion is integralwith the container wall and projects outwardly from the plane of thecontainer wall adjacent the fracturable web and is adapted to effect, inresponse to digitally applied inwardly directed pressure thereon,relative displacement of the lip and rim to strain the web and initiatefracture thereof.

In its narrower aspects the invention includes the formation of afracturable web by moving metal adjacent a predetermined linesubstantially perpendicular to the surface of the sheet while squeezinga zone of metal along such line between substantially parallel diesurfaces which are disposed at an angle to the plane of the containerwall. Such squeezing of the container wall along the zone of metalextrudes metal laterally from such line to produce a bulge forming atleast a part of said deflectable portion in the container wall which canbe flexed to cause relative movement of the metal on opposite sides ofthe fracturable web and thereby facilitate initiation of rupturethereof.

Among the advantages of the subject invention are the provisions of ametal container closure construction that exceeds the stringent presentday interrelated commercial economic and performance criteria and whichalso satisfies current ecology based governmental regulations. Morespecific advantages include the provision of a highly reliable endclosure of markedly reduced metal content that can be fabricated with aminimal number of fabricating steps at extremely high production rateswith simple tooling. Further advantages include the provision of an endclosure that can be opened by application of modest amounts of digitallyapplied pressure without the use of auxiliary tools and the overcomingof ecology based objection to present day Fraze type severable pull tabclosures through inward displacement of a closure panel sized to belarger than the resulting opening in the container wall.

The object of this invention is the provision of an improved method andapparatus for forming and construction for a digitally openablecontainer end closure.

Accordingly, another object of the invention is to provide a tablesscontainer wall which can be opened with the fingers.

Another object of the invention is to provide a method of forming acontainer wall with a fracturable web in it which can be easily rupturedwhen force is applied against one surface of the container wall.

Another object of the invention is to provide a method of forming afracturable web in a container wall by displacing metal at right anglesto the plane of the container wall while squeezing a zone of metal toprevent complete severance of the container wall during suchdisplacement of metal.

A further object of the invention is to provide a method of deforming asheet of metal to provide a selectively contoured fracturable web thatcan be ruptured without the need for a special cool or a pull tabattached to the severable portion of the sheet.

Another object of the invention is to provide a container wall with afracturable web in it defining a removable panel and an adjacentflexible or deflectable bulge for displacing portions of the containerwall to facilitate initiation of rupture of the web.

Another object of the invention is to provide a container wall with afracturable web in it defining a removable panel with an edge portion ofthe removable panel and an adjacent edge portion of the container walllying in substantially parallel planes, and further including adeflectable bulge in the container wall for selectively displacingportions of the container wall to cause relative movement of the metalon opposite sides of the fracturable web to initiate rupture or fractureof the web.

BRIEF DESCRIPTION OF THE DRAWINGS end of the invention seamed on acontainer and illustrating finger pressure applied to an outwardly domedor bulged panel to initiate rupture of the fracturable web in the canend,

FIG. 4 is a section view similar to FIG. 3 and showing the can end afteropening,

FIG. 5 is a perspective view of an alternative embodiment of a closureof the invention,

FIG. 6 is a cross section through the closure of FIG.

FIG. 7 is a cross section illustrating tools for deforming a containerwall in accordance with the invention,

FIG. 8 is an enlarged cross sectional view of a portion of the toolsfrom FIG. 7 illustrating an intermediate stage in the forming ofafracturable web in a container wall,

FIG. 9 is a cross sectional view similar to FIG. 7 illustrating furtherdisplacement of the die members in the formation of a fracturable web ina container wall, and

FIG. 10 is an enlarged cross sectional view of a portion of a presentlypreferred embodiment of a container wall constructed in accordance withprinciples of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to FIGS. 1 and 2, acontainer wall or can end 10 is shown which includes a substantiallyplanar central panel 12, a peripheral groove 14 around the panel anupstanding wall 16 outwardly of the groove, a flange 18 extendingoutwardly from the top of the upstanding wall and a curled edge 20 onthe outer end of the flange. Such general construction of a peripherallychimed can end is typical of can ends which are adapted to be sealed oncontainer bodies by conventional double seaming operations.

In order to facilitate understanding of the subject invention and in theinterest of clarity, the terms inwardly and outwardly will be hereinemployed to delineate directions relative to the interior and exteriorrespectively of a cylindrical container having the end closure ofinterest mounted on the end thereof.

In accordance with this invention, can end further includes at leastone, and preferably two, inwardly displaceable opening panels 22 ofequal size defined by weakening lines 24 in the form of fracturable websin central panel 12. Panels 22 are designed to be opened by displacingthem into a container on which can end 10 is sealed to form a pouringopening and/or a vent in the can end. In the embodiment selected forillustration in FIGS. 1 through 4, each fracturable web 24 may beC-shaped with a bridge of metal between the ends of the line providing ahinge 26 which prevents complete separation of the opening panel 22 fromcontainer end 10. Hinge 26 between the ends of the fracturable web 24may be slightly weakened by a shallow score line or the like, but mayalso be unweakened for some applications. In case of accidental ruptureof the web 24 due to excessively high internal pressures in a container,hinge 26 will prevent complete separation of a removable panel 22 fromcan end 10. Hinge 26 also normally prevents the panel 22 from droppinginto the container after inward displacement thereof.

As illustrated in FIG. 1, each opening panel 22 is substantially smallerthan the can end 10 in which it is provided and constitutes a minorportion, or less than half, of the area of the can end.

It is a feature of a container end constructed in accord with theprinciples of this invention that at least a marginal edge portion 28 ofopening panel 22 adjacent the fracturable web 24 be disposed withrespect to an adjacent marginal edge portion 30 of central panel 12 onthe other side of the web such that opposite faces of such two marginaledge portions 28 and 30 are disposed in nearly the same plane. In theembodiment selected for illustration in FIGS. 1-4, such displacementresults in the top surface of the edge portion 28 of the opening panel22 being disposed in nearly the same plane as is the bottom surface ofedge portion 30 of the adjacent portion of central panel 12 disposed onthe other side of the fracturable web.

It is another feature of this invention that the central panel 12 has abulge or bulges formed in it adjacent the fracturable web 24 as is bestillustrated in FIGS. 2 and 9. As will be explained, flexing or otherdigitally induced displacement of such bulge or bulges, which constituteat least part of a deflectable portion of the container wall,facilitates rupture of the web 24 by producing relative movement ofmetal on opposite sides of the web to strain the residual metal andinitiate its failure. In can end 10, a bulge 32 may be formed adjacentremovable panel 22 or a bulge 33 may be formed within the opening panel22', as will be described.

Depending on the intended use of a container end eg on pressurized orunpressurized cans or on automatically ventable cans; the adjacentportions of metal on opposite sides of the fracturable web 24 and theflexible deflectable portions 32 and 33 may be formed either outwardlyor inwardly directed with respect to the initially undisplaced metal inthe container wall. In the can end 10 illustrated in FIGS. 1-4, which isadapted to be sealed on a container for holding relatively high internalpressures, the marginal edge portion 28 of opening panel 22,haspreferably been displaced downward with respect to the adjacent portion30 of central panel 12 on the opposite side of the fracturable websothat the web will have a greater resistance against rupture due tointernal pressure in the container than it will have against rupture dueto external pressure applied against opening panel 22. The difference inresistance to rupture of a weakening line depending on the direction offorce was previously broadly disclosed in the Punte and Geiger US. Pat.Nos. 2,187,433 and 3,362,569, and is believed to result from an overlapof metal on opposite sides of a weakening line.

Deflectable portion 32 is preferably formed outwardly with respect tothe initially undisplace surface of can end 10 so that finger pressureapplied against opening panel 22 or more desirably against saiddeflectable portion 32 will cause flexing and selective displacementthereof to facilitate initial fracture of the web 24 as will now beexplained. As illustrated in FIG. 3, depressing the illustratedoutwardly domed opening panel 22 causes flexing and displacement of atleast portions of central panel 12. While not fully understood at thepresent time, it is believed that this flexing of portions of centralpanel 12 causes relative movement of adjacent portions of metal onopposite sides of the fracturable web 24 to thereby stress and fracturethe thin residual of metal constituting such web. Such flexingdisplacement of portions of container panel 12 is also believed to causesome bending of the thin residual of metal constituting the web tofurther contribute to the initiation of fracture thereof. As openingpanel 22 is further depressed, the web 24 around the panel 22 continuesto separate so that the panel may be hinged inwardly into the containeras illustrated in FIG. 4. When both panels 22 have been so opened, oneopening can be used for pouring or drinking from the container, and theother opening will vent air into the container.

FIGS. 5 and 6 illustrate another embodiment of a closure incorporatingthe principles of this invention which is particularly adapted forclosing a bottle or other container for food which may be vacuum packed.Closure 34 includes an end wall 36, a peripheral skirt 38 with a curlededge 40 thereon for engaging under a retaining bead or lugs on acontainer. In accordance with this invention, closure 34 furtherincludes an upwardly domed deflectable button 42 in end wall 36 and twofracturable webs 44 formed in the button near its top. Fracturable webs44 may be arcuate in shape and concave toward the periphery of theclosure leaving a bridge 46 of unweakened metal between the fracturablewebs. In this embodiment of the invention, the metal between thefracturable webs 44 is preferably displaced outwardly with respect toadjacent metal on the opposite sides thereof as illustrated in FIG. 6.

When it is desired to open a container on which closure 34 is sealed,bridge 46 may be inwardly displaced to cause failure of at least one ofwebs 44 and thereby release the vacuum in the container. Releasing thevacuum in a container on which closure 34 is sealed will obviouslyfacilitate removal of the closure from the container by freeing theclosure to be more easily moved with respect to the container. It isbelieved that inward displacement of bridge 46 causes relative movementof metal on opposite sides of fracturable webs 44 to stress the thinresidual of metal in the web and thereby facilitate initiation of itsrupture.

FIGS. 7, 8 and 9 illustrate exemplary tools and a preferred method forforming the particularly contoured fracturable web in accordance withthe invention. Such exemplary tools comprise an annular top die 48 andan annular bottom die 50 between which a sheet metal container wall 10is introduced to have the fracturable web formed therein, an auxiliaryouter die means 49 and an optionally employable inner doming tool 51 forcontrolling the direction in which deflectable portion 32 and domedopening panel 22 are formed in the container wall. Top die 48 has afirst substantially planarhorizontal bottom face or base surface 52, aninner face 53 inclined upwardly from base surface 52 to permit theformation of an upwardly domed opening panel, and a second and angularlydisposed substantially planar metal extruding surface or face 54 whichpreferably extends outwardly from the first base surface atapproximately a 45 angle, although limited angular departure therefrommay apparently be tolerated. The first base surface 52 and second metalextruding surface 54 of die 48 meet at a relatively sharp corner 56 sothat a similar sharp corner will be formed in container wall 10.Preferably the corner 56 between the first and second die surfaces 52and 54 has a radius of less than 0.001 inch, but may tolerate a radius,as for example as would be occasioned by wear, of up to about 0.005 inchon tools for forming a fracturable web in rigid aluminum alloy containersheet having a thickness in a range of 0.010 inch to 0.015 inch which istypical of sheet used in the production of can ends.

Bottom die 50 has a first substantially planar base surface or top face58, a downwardly inclined outer face 59 to permit the formation of adeflectable portion 32 externally adjacent the opening panel 22 and asecond and angularly disposed substantially planar metal extrudingsurface or inner face 60 extending downwardly from the first basesurface 58 at approximately a 45 angle. Base surface 58 and metalextruding surface 60 also preferably meet at a relatively sharp corner62 as do the die faces in top die 48. Metal extruding surfaces 54 and 60on top and bottom dies 48 and 50 are preferably substantially parallel,although limited departure therefrom can apparently be tolerated. lnnerdoming tool 51 may further have an upwardly projecting dome 64 on it toform an outwardly domed opening panel 22 which can be concurrentlyformed therewith. The auxiliary die means 49 and inner doming tool 51may be integral parts of tools 48 and 50 respectively, or for ease offabrication may be separate parts as illustrated, but are preferablymoved as unitary assemblies during practice of the invention. Innerdoming tool 51 may be omitted from the tools where the presentlypreferred inwardly domed opening panel 22 is to be formed.

Auxiliary outer die means 49 is disposed on the same side of containerwall as is upper die member 48 and has a metal shaping base surface 49afacing the same general direction as does first base surface 52 of upperdie member 48 and is in laterally spaced relation with the first basesurface 58 on the lower die member 50.

As tools 48, 49, 50 and 51 (when included) are moved against containerwall 10 which has been introduced between the dies, metal from thecontainer wall is first drawn or stretched over dome 64 on inner domingtool 51. As the dies continue to close, the first base surface 52 andthe second metal extruding surface 54 of the top die member 48 arelineally displaced toward the second angularly disposed metal extrudingsurface 60 and first base surface 58 respectively of the second diemember 60 and with the corners 56 and 62 being maintained in laterallyspaced relation as described above. Following initial engagement of thetop die member 48 with interposed metal sheet, metal from container wall10 begins to be displaced or moved by the base die surfaces 52 and 58substantially perpendicular, or a right angles, to the initiallyundisplaced surface of the container wall. When base die surfaces 52 and58 have closed to within approximately threefourths to two-thirds of thethickness of container wall 10, metal begins to be extruded from betweenthe angularly offset metal extruding surfaces 54 and 60 on the dies. Upto that point, the metal in container wall 10 is merely reformed aroundcorners 56 and 62 on the dies.

As dies 48 and 50 continue to close with respect to one another, metalin container wall 10 is squeezed between the metal extruding surfaces 54and 60 of the dies to cause lateral flow or extrusion of metal away fromthe fracturable web while metal is also being displaced at substantiallyright angles to the initially undisplaced surface of the container wall.The described lineal displacement of the top die member 48 toward thelower die member 50 continues until the first base surface 52 thereof isdisposed substantially coplanar with the first base surface 58 of lowerdie member 50. [t is believed that this lateral flow or extrusion ofmetal away from the fracturable web which is being formed is importantin preventing cracks from forming in, and premature severance of theweb. 1n the absence of such extrusion, metal may be sheared or cut bythe tools as is done in typical blanking or punching operations in whichthe metal is separated or sheared along the line of the tools before thedies have completely penetrated the metal. The present inventionsubstantially eliminates the formation of cracks or failures in thefracturable web because metal is extruded laterally away from the webduring the right angle displacement of metal to cause lateral flow ofmetal approximately as fast as the metal is being displaced at rightangles so that the metal is not sheared or separated by such right angledisplacement. Experience to date indicates that in the practice of thisinvention, container ends of the type disclosed can be formed at highrates of press operation to produce 300 or more ends per minute per dieset up with few or no defective can ends.

Lateral metal flow away from the fracturable web that is being formedalso produces an increased surface area of metal in a can end forforming the desired deflectable portion in the metal adjacent the web.As explained above, such deflectable portion 32 is believed tofacilitate rupture of the fracturable web. 1n the tools illustrated inFIGS. 7-9, the auxiliary die means 49 and the inner doming tool 51respectively control the direction in which the increased area of metalis formed so that deflectable portion 32 and domed opening panel 22project outwardly with respect to the original undisplaced surface ofthe can end. Obviously, for other can ends or closure applications,similar tools could also control the metal working so that the bulges ordeflectable portions would be formed downward (i.e., inwardly) on one orboth sides of the fracturable web if desired.

After inner doming tool 51 has initiated outward doming of opening panel22, lateral extrusion of metal produced by the formation of fracturableweb 24 further domes the opening panel so that the metal in the panel isspaced above dome 64 on the doming tool 51 as is illustrated in FIG. 9.Auxiliary die means 49 controls the formation of the preferred outwardlyprojecting deflectable portion 32 adjacent the fracturable web 24 byrestraining the metal distal the fracturable web so that the metal bowsupward over bottom die 50 as is 9 also illustrated in FIG. 9. In formingthe deflectable portion 32, the auxiliary die means 49 is lineallydisplaced to selectively move the base surface 49a thereof intopredetermined longitudinally offset relations with the first basesurface 58 of lower die member 50 in the direction of die displacement.

It is believed that lateral extrusion of metal during formation of theparticularly contoured fracturable web 24 in accordance with theprinciples of this invention results in the formation of complexresidual stresses in the web probably having a substantial componentthereof in shear which may interact with the stresses produced by inwarddisplacement of the deflectable portions to contribute in initiatingrupture of the fracturable web. Such residual stresses apparently actwithin the fracturable web 24 to make it easier to initiate its rupture.

In the practice of this invention, the amount of lateral spacing .x"between the corners 56 and 62 in the horizontal direction may varydepending upon the alloy, temper and thickness of the metal in containerwall, the angle of the metal extruding surfaces 54 and 60, and theresidual thickness of metal to be left in the fracturable web amongother factors. Such lateral spacing is preferably in the range of l/4 to1/6 of the thickness of the container wall in which the fracturable webis formed, but may be from 5 percent to 50 percent of the metalthickness for some applications. In the exemplary practice of theinvention, an overlap x of die surfaces 54 and 60 of approximately0.0032 inch has been found to work well in forming a fracturable web ina container wall made from a sheet of hard temper aluminum base alloy0.013 inch thick. In that example, the dies were moved toward oneanother until base surfaces 52 and 58 were within approximately 0.001inch of coplanar orientation. This produced a fracturable web with athin residual of metal approximately 0.004 inch thick with no crackstherein.

FIG. illustrates a presently preferred configuration of a metal endclosure incorporating the principles of this invention. There isprovided a central panel 12 having a least one circular and relativelyrigid opening panel 22 contoured to include an inwardly domed centerportion 33 bounded by a rim 28 peripherally terminating in a fracturableweb 24. The web 24 interconnects the rim 28 with a lip 30 of an integraloutwardly projecting deflectable portion 32 of generally frustoconicalconfiguration surrounding the opening panel 22 in the adjacent portionof the container wall. Preferably, rim 28 has a substantially planarupper surface 70 which terminally intersects an angularly inclinedsurface 72 defining the inner marginal edge of lip 30 of deflectableportion 32 in an exposed corner 74. Lip 30 has a substantially planarundersurface 76 disposed in substantially coplanar relation with theupper surface 70 of rim 28 and which terminally intersects an angularlyinclined surface 78 defining the outer marginal edge of the rim 28 ofthe panel 22 in a second corner 80. The corners 74 and 80 are disposedin predetermined laterally spaced relation and define therebetween thelateral extent of the fracturable web 24.

Each opening panel 22 includes means for imparting greater rigidity tothe opening pane] than that of the deflectable portion. In the preferredembodiment, the domed shape of each opening panel provides the desiredincrease in rigidity. The size of the opening panel is also believed tobe a factor in its rigidity. It will be apparent to those skilled in theart that other means 10 such as greater metal thickness, embossments orthe like can be employed to impart the desired increased rigidity to theopening panel.

Deflectable portion 32 in container end 10 is adapted to effect, inresponse to inwardly directed digitally applied pressure a relativedisplacement of lip 30 with respect to rim 28 to strain fracturable web24 and initiate fracture thereof to permit inward displacement of aseparated opening panel of greater rim size than the size of the openingwhich is formed in the end. Such inwardly directed digital pressure isbest applied against the end 10 adjacent web 24 and preferably againstthe raised lip 30 of the deflectable portion 32 as is illustrated inFIG. 10. Such inward pressure against the deflectable portion 32 appearsto move the lip 30 relative to the rim 28 of the relatively rigidopening panel 22 to strain the fracturable web 24 and initiate fracturethereof. As pointed out above, the opening panel 22 is preferably ofrelatively rigid character to resist bending thereof and thereby insurethat the displacement of the deflectable portion 32 will createsufficient relative displacement of the lip 30 thereof with respect tothe rim 28 of the opening panel 22 to initiate web fracture. The lateralspacing corners of 74 and are selected to define a web of at least apredetermined minimal extend sufficient to maintain its structuralintegrity during exposure to variations in the magnitude of the residualstress therein occasioned by normal container handling and usage andless than a predetermined maximum extent that would preclude saiddisplacement induced fracture thereof in response to said digitallyapplied inwardly directed pressure.

While the mechanics underlying the mode of operation of the subjectconstruction are not well understood at the present ime, it is believedthat complex residual stresses are introduced into the particularlycontoured fracturable web by the metal displacement effected during theformation thereof. It is further believed that the relative displacementof the deflectable portion induced by the inwardly directed digitallyapplied pressure introduces a further complex stress pattern of varyingcharacter into said web and that localized web fracture is initiated byselectively located and probably localized interactions thereof with theformationcreated residual stresses extant therein. 7

It is therefore seen that a container wall and a method of forming thesame are provided which offer improved opening characteristics andimproved resistance to the formation of cracks in the fracturable web inthe container wall. Metal is moved substantially at right angles to theinitially undisplaced surface of the container wall along thefracturable web while metal is extruded laterally away therefrom. Theextrusion of metal causes lateral metal flow which is approximately asfast as the right angle displacement of metal during at least the latterpart of the forming operation to thereby avoid shearing the metal, andfurther forms a deflectable portion in the container wall whosedigitally induced displacement initiates web fracture.

The invention is particularly well suited for use with container wallsmade of work hardened aluminum base alloy sheet material in thethickness range of 0.010 inch to 0.015 inch and which is at leastquarter hard, and preferably at least three-quarter hard temper or is ofextra hard temper alloy which has been partially annealed as a result ofheating it to cure a protective coating thereon. Quarter hard aluminumalloy sheet will generally have a yield strength which is at leastone-half the yield strength for the same alloy in a full hard condition,and two or more times the yield strength for the product in a fullyannealed or recrystallized condition. It is believed that such workhardened alloy sheet material is particularly well suited to practice ofthe invention because material of the specified hardness is required toassure conversion of the inwardly directed digitally applied pressuresinto selectively directed displacement of the lip of the deflectableportion relative to the rim of the relatively rigid opening panel. It isfurther believed that work hardened aluminum alloy will also result inthe presence of greater residual stresses in the metal, both as to thoseintroduced in the initial formation of the fracturable web and thoseintroduced by relative metal displacement as described above.

Experience to date has indicated that opening panels having diameters inthe range of about one-eighth inch to three-quarters inch provideadequate pour and venting rates and also result in adequate lateralmetal extrusion during forming to produce deflectable portions ofdesired size and configuration. With respect to such deflectableportions, it is believed that an angle inclination in a range of about 5to degrees to the general plane of an end closure provides an adequatetogglelike action to effect the necessary displacement of the lipportion relative to the opening panel rim portion to initiate webfracture.

Although a preferred embodiment of a container wall and a preferredmethod and apparatus for forming the same have been illustrated anddescribed, it will be apparent to those skilled in the art that numerousvariations could be made therein without departing from the invention.

What is claimed is:

1. A peripherally chimed sheet metal container component having a wallwith at least one inwardly displaceable opening panel thereinnon-concentric with the peripheral chime around the container componentand constituting a minor portion of the component, said opening panelhaving an integral rim therearound peripherally terminating in afracturable web defining a locus of separation of said opening panelfrom the adjacent portion of said wall,

an integral deflectable portion adjacent said opening panel andprojecting outwardly from the general plane of the wall of saidcontainer component, said deflectable portion terminating in a lip onthe marginal edge thereof toward said web integrally interconnected withthe rim of said opening panel and defining therewith said fracturableweb,

the rim of said opening panel including an outwardly exposed surfaceterminally intersecting the outwardly exposed marginal edge of the lipof said deflectable portion in an outwardly exposed corner,

said deflectable portion having a portion of the undersurface thereofterminally meeting the undersurface of the outer marginal edge of saidrim in predetermined spaced relation with said exposed corner to definetherebetween the extent of said fracturable web,

said opening panel including means for imparting greater rigiditythereto than that of said deflectable portion disposed adjacent theretoto effect an initiation, in response to digitally applied localizedinwardly directed pressure against said deflectable 12 portion at alocation spaced from the peripheral chime around the containercomponent, of relative displacement of said lip relative to said rim tostrain said web and induce fracture thereof to permit inwarddisplacement of a separated opening panel.

2. A sheet metal end closure for a container comprismg a generallyplanar wall portion peripherally chimed for securement to a containerbody, at least one inwardly displaceable relatively rigid opening panelintegrally included therein non-concentric with the peripheral chimearound the closure and constituting a minor portion of the closure, saidopening panel having a center portion and an integral rim therearoundperipherally terminating in a fracturable web defining a locus ofseparation of said opening panel from said wall portion,

an integral deflectable portion adjacent said opening panel andprojecting outwardly from the general plane of said wall portion, saiddeflectable portion terminating in a lip on the marginal edge thereoftoward said web integrally interconnected with the rim of saiddisplaceable opening panel and defining therewith said fracturable web,

said rim of said opening panel including an outwardly exposed surfaceterminally intersecting the outwardly exposed marginal edge of the lipof said deflectable portion in an outwardly exposed corner,

the undersurface of said deflectable portion terminally meeting theundersurface of the outer marginal edge of said rim of said openingpanel in predetermined spaced relation with said exposed corner todefine therebetween the extent of said fracturable web,

said opening panel including means for imparting greater rigiditythereto than that of said deflectable portion disposed adjacent theretoto effect an initiation, in response to digitally applied localizedinwardly directed pressure against said deflectable portion at alocation spaced from the peripheral chime around the closure, ofrelative displacement of the lip thereof relative to the rim of saidopening panel to stress said web and initiate fracture thereof to permitinward displacement of a separated opening panel of greater rim sizethan the size of the opening formed in said wall portion as defined bythe inner marginal edge of the lip of said deflectable portion.

3. A closure as set forth in claim 2 wherein said deflectable portion isinclined from the general plane of said wall portion toward said lip atan angle in the range of 5 to 15.

4. A closure as set forth in claim 2 wherein said opening panel is ofgenerally circular configuration and said deflectable portion isannularly disposed in surrounding relation therewith.

5. A closure as set forth in claim 2 wherein the center portion of saidopening panel is domed.

6. A closure as set forth in claim 2 wherein said wall portion includesat least two circular openings panels of equal diameter.

7. A closure as set forth in claim 2 wherein the upper surface of therim of said opening panel is in substantially coplanar relation with theundersurface of the lip of said deflectable portion.

8. A closure as set forth in claim 2 wherein said wall portion compriseswork hardened aluminum alloy '13 which is at least three-quarter hard.

9. A closure as set forth in claim 2 wherein said opening panel iscircular in shape and has a-diameter in the range of inch to $6. inch.

10. A closure as set forth in claim 2 wherein said fracturable webinterconnects the rim of said opening panel and the lip of saiddeflectable portion outwardly of the general plane of said wall portion.

11. A sheet metal end closure of work hardened aluminum alloy suitablefor a pressurized fluid container comprising a generally planar wallportion peripherally chimed for securement to a container body, at leastone inwardly displaceable relatively rigid opening panel integrallyincluded therein non-concentric with the peripheral chime around theclosure and constituting a minor portion of the closure said openingpanel having a domed center portion and a selectively shaped rimtherearound peripherally terminating in a particularly contoured,residually stressed fracturable web defining a locus of separation ofsaid opening panel from said wall portion,

an integral inclined deflectable portion adjacent said opening panel andprojecting outwardly from the general plane of said wall portion andterminating in a particularly shaped lip on the marginal edge thereoftoward said web integrally interconnected with the rim of saiddisplaceable opening panel and defining therewith said fracturable web,

said rim of said opening panel including an upper planar surfaceterminally intersecting an angularly inclined surface defining the innermarginal edge of the lip of said deflectable portion in a firstoutwardly exposed corner,

said lip of said deflectable portion including a planar undersurfacedisposed substantially coplanar with the upper surface of said rim ofsaid opening panel and terminally intersecting an angularly inclinedsurface defining the outer marginal edge of the rim of said openingpanel in a second corner disposed in predetermined laterally spacedrelation with said first corner to define, by the overlap therebetween,the lateral extent of said fracturable web,

said opening panel including means for imparting greater rigiditythereto than that of said deflectable portion to effect in response todigitally applied inwardly directed pressure against the deflectableportion at a location spaced from the peripheral chime around theclosure, a directional relative displacement of the lip thereof with therim of said opening panel to initiate fracture of said web to permitinward displacement of a separated opening panel of greater rim sizethan the size of the opening formed in said wall portion as defined bythe terminal edge of the angularly inclined surface of the lip of saiddeflectable portion,

the lateral spacing of said first and second corners defining a web ofat least a predetermined minimal extent sufficient to maintain itsstructural integrity during exposure to variations in the magnitude ofthe residual stress therein occasioned by normal container handling andusage and less than a predetermined maximum extent that would precludesaid fracture thereof in response to said digitally applied inwardlydirected pressure.

12. A sheet metal end closure as set forth in claim 11 wherein saidplanar wall portion includes two displaceable opening panels of circularconfiguration, each surrounded by a deflectable portion of annularconfiguration.

13. A sheet metal end closure as set forth in claim 11 wherein saidopening panel is inwardly domed.

14. A sheet metal end closure as set forth in claim 11 wherein saidangularly inclined surface 'of the lip of the deflectable-portion isdisposed substantially parallel to the angularly inclined surface of therim of said opening panel.

15. A sheet metal end closure as set forth in claim 14 wherein each ofsaid angularly inclined surfaces is disposed at an angle of about 45 tothe planar surface associated therewith.

16. A'sheet metal end closure as set forth in claim 1 1 wherein saidfracturable web is interrupted to form a hinge element of greaterthickness than the fracturable web.

17. A sheet metal end closure as set forth in claim 11 wherein the workhardened aluminum alloy forming said planar wall portion has a thicknessin the range of 0.010 inch to 0.0l5 inch.

18. A sheet metal end closure as set forth in claim 1 1 wherein saidwall portion comprises work hardened aluminum alloy which is at leastthree-quarter hard.

19. A sheet metal end closure as set forth in claim 1 1 wherein saidfirst and second corners have a permitted difference in elevation nogreater than 0.001 inch.

20. A sheet metal end closure as set forth in claim 11 wherein saidopening panel is of generally circular configuration and saiddeflectable portion disposed thereabout is of frusto-conicalconfiguration.

21. A sheet metal end closure as set forth in claim 11 wherein theresidual stresses at the locus of separation are of such character andmagnitude as to initiate fracture of the web upon localized interactionthereof with stresses induced by digitally applied pressure.

22. A sheet metal end closure as set forth in claim 11 wherein saidopening panel is circular in shape and has a diameter in the range of 4;inch to inch.

23. A sheet metal end closure of at least three-quarter hard temperaluminum alloy of a thickness in the range of 0.010 inch to 0.0l5 inchsuitable for a pressurized fluid container comprising a generally planarwall portion peripherally chimed for securement to a container body,

at least one hinged inwardly displaceable relatively rigid circularopening panel integrally included therein having an inwardly domedcenter portion and a selectively shaped rim peripherally terminating ina particularly contoured, residually stressed and annularly shapedfracturable web defining a locus of separation of said hinged openingpanel from said wall portion,

an integral inclined annularly shaped deflectable portion offrusto-conical configuration surrounding said opening panel andprojecting outwardly from the plane of said wall portion and terminatingin a particularly shaped lip integrally interconnected with the rim ofsaid displaceable opening panel and defining therewith said fracturableweb,

said rim of said opening panel including an upper planar surfaceterminally intersecting at an angle of about an angularly inclinedsurface defining the inner marginal edge of the lip of said deflectableportion in a first exposed corner,

said lip of said deflectable portion including a planar undersurfacedisposed substantially coplanar with the upper surface of the rim ofsaid opening panel and terminally intersecting at an angle of about 135an angularly inclined surface defining the outer marginal edge of therim of said opening panel in a second corner disposed in predeterminedlaterally spaced relation with said first corner to define, by theoverlap therebetween, the lateral extent of said fracturable web, andhaving a permitted difference in elevation therebetween of no greaterthan 0.001 inch,

said deflectable portion being adapted to effect, in

response to digitally applied inwardly directed pressure, a directionalrelative displacement of the lip thereof with the rim of said openingpanel to interact with the residual stresses extant in said webangularly inclined surface of the lip of said deflectable portion,

the lateral spacing of said first and second corners being no more than0.004 inches and defining a web of at least a predetermined minimalextent sufficient to maintain its structural integrity during exposureto variations in the magnitude of the residual stress therein occasionedby normal container handling and usage and less than a predeterminedmaximum extent that would preclude said fracture thereof in response tosaid digitally applied inwardly directed pressure.

24. A sheet metal end closure as set forth in claim 23 wherein saidplanar wall portion includes two displaceable opening panels of circularconfiguration, each surrounded by a deflectable portion of annularconfiguration.

and initiate fracture thereof to permit inward displacement of aseparated opening panel of greater rim size than the size of the openingformed in said wall portion as defined by the terminal edge of the

1. A peripherally chimed sheet metal container component having a wallwith at least one inwardly displaceable opening panel thereinnonconcentric with the peripheral chime around the container componentand constituting a minor portion of the component, said opening panelhaving an integral rim therearound peripherally terminating in afracturable web defining a locus of separation of said opening panelfrom the adjacent portion of said wall, an integral deflectable portionadjacent said opening panel and projecting outwardly from the generalplane of the wall of said container component, said deflectable portionterminating in a lip on the marginal edge thereof toward said webintegrally interconnected with the rim of said opening panel anddefining therewith said fracturable web, the rim of said opening panelincluding an outwardly exposed surface terminally intersecting theOutwardly exposed marginal edge of the lip of said deflectable portionin an outwardly exposed corner, said deflectable portion having aportion of the undersurface thereof terminally meeting the undersurfaceof the outer marginal edge of said rim in predetermined spaced relationwith said exposed corner to define therebetween the extent of saidfracturable web, said opening panel including means for impartinggreater rigidity thereto than that of said deflectable portion disposedadjacent thereto to effect an initiation, in response to digitallyapplied localized inwardly directed pressure against said deflectableportion at a location spaced from the peripheral chime around thecontainer component, of relative displacement of said lip relative tosaid rim to strain said web and induce fracture thereof to permit inwarddisplacement of a separated opening panel.
 2. A sheet metal end closurefor a container comprising a generally planar wall portion peripherallychimed for securement to a container body, at least one inwardlydisplaceable relatively rigid opening panel integrally included thereinnon-concentric with the peripheral chime around the closure andconstituting a minor portion of the closure, said opening panel having acenter portion and an integral rim therearound peripherally terminatingin a fracturable web defining a locus of separation of said openingpanel from said wall portion, an integral deflectable portion adjacentsaid opening panel and projecting outwardly from the general plane ofsaid wall portion, said deflectable portion terminating in a lip on themarginal edge thereof toward said web integrally interconnected with therim of said displaceable opening panel and defining therewith saidfracturable web, said rim of said opening panel including an outwardlyexposed surface terminally intersecting the outwardly exposed marginaledge of the lip of said deflectable portion in an outwardly exposedcorner, the undersurface of said deflectable portion terminally meetingthe undersurface of the outer marginal edge of said rim of said openingpanel in predetermined spaced relation with said exposed corner todefine therebetween the extent of said fracturable web, said openingpanel including means for imparting greater rigidity thereto than thatof said deflectable portion disposed adjacent thereto to effect aninitiation, in response to digitally applied localized inwardly directedpressure against said deflectable portion at a location spaced from theperipheral chime around the closure, of relative displacement of the lipthereof relative to the rim of said opening panel to stress said web andinitiate fracture thereof to permit inward displacement of a separatedopening panel of greater rim size than the size of the opening formed insaid wall portion as defined by the inner marginal edge of the lip ofsaid deflectable portion.
 3. A closure as set forth in claim 2 whereinsaid deflectable portion is inclined from the general plane of said wallportion toward said lip at an angle in the range of 5* to 15*.
 4. Aclosure as set forth in claim 2 wherein said opening panel is ofgenerally circular configuration and said deflectable portion isannularly disposed in surrounding relation therewith.
 5. A closure asset forth in claim 2 wherein the center portion of said opening panel isdomed.
 6. A closure as set forth in claim 2 wherein said wall portionincludes at least two circular openings panels of equal diameter.
 7. Aclosure as set forth in claim 2 wherein the upper surface of the rim ofsaid opening panel is in substantially coplanar relation with theundersurface of the lip of said deflectable portion.
 8. A closure as setforth in claim 2 wherein said wall portion comprises work hardenedaluminum alloy which is at least three-quarter hard.
 9. A closure as setforth in claim 2 wherein said opening panel is circular in shape and hasa diameter in the range of 1/8 inch to 3/4 inch.
 10. A closure as setforth in claim 2 wherein said fracturable web interconnects the rim ofsaid opening panel and the lip of said deflectable portion outwardly ofthe general plane of said wall portion.
 11. A sheet metal end closure ofwork hardened aluminum alloy suitable for a pressurized fluid containercomprising a generally planar wall portion peripherally chimed forsecurement to a container body, at least one inwardly displaceablerelatively rigid opening panel integrally included thereinnon-concentric with the peripheral chime around the closure andconstituting a minor portion of the closure said opening panel having adomed center portion and a selectively shaped rim therearoundperipherally terminating in a particularly contoured, residuallystressed fracturable web defining a locus of separation of said openingpanel from said wall portion, an integral inclined deflectable portionadjacent said opening panel and projecting outwardly from the generalplane of said wall portion and terminating in a particularly shaped lipon the marginal edge thereof toward said web integrally interconnectedwith the rim of said displaceable opening panel and defining therewithsaid fracturable web, said rim of said opening panel including an upperplanar surface terminally intersecting an angularly inclined surfacedefining the inner marginal edge of the lip of said deflectable portionin a first outwardly exposed corner, said lip of said deflectableportion including a planar undersurface disposed substantially coplanarwith the upper surface of said rim of said opening panel and terminallyintersecting an angularly inclined surface defining the outer marginaledge of the rim of said opening panel in a second corner disposed inpredetermined laterally spaced relation with said first corner todefine, by the overlap therebetween, the lateral extent of saidfracturable web, said opening panel including means for impartinggreater rigidity thereto than that of said deflectable portion to effectin response to digitally applied inwardly directed pressure against thedeflectable portion at a location spaced from the peripheral chimearound the closure, a directional relative displacement of the lipthereof with the rim of said opening panel to initiate fracture of saidweb to permit inward displacement of a separated opening panel ofgreater rim size than the size of the opening formed in said wallportion as defined by the terminal edge of the angularly inclinedsurface of the lip of said deflectable portion, the lateral spacing ofsaid first and second corners defining a web of at least a predeterminedminimal extent sufficient to maintain its structural integrity duringexposure to variations in the magnitude of the residual stress thereinoccasioned by normal container handling and usage and less than apredetermined maximum extent that would preclude said fracture thereofin response to said digitally applied inwardly directed pressure.
 12. Asheet metal end closure as set forth in claim 11 wherein said planarwall portion includes two displaceable opening panels of circularconfiguration, each surrounded by a deflectable portion of annularconfiguration.
 13. A sheet metal end closure as set forth in claim 11wherein said opening panel is inwardly domed.
 14. A sheet metal endclosure as set forth in claim 11 wherein said angularly inclined surfaceof the lip of the deflectable portion is disposed substantially parallelto the angularly inclined surface of the rim of said opening panel. 15.A sheet metal end closure as set forth in claim 14 wherein each of saidangularly inclined surfaces is disposed at an angle of about 45* to theplanar surface associated therewith.
 16. A sheet metal end closure asset forth in claim 11 wherein said fracturable web is interrupted toform a hinge element of greater thickness than the fracturable web. 17.A sheet metal end closure as set forth in Claim 11 wherein the workhardened aluminum alloy forming said planar wall portion has a thicknessin the range of 0.010 inch to 0.015 inch.
 18. A sheet metal end closureas set forth in claim 11 wherein said wall portion comprises workhardened aluminum alloy which is at least three-quarter hard.
 19. Asheet metal end closure as set forth in claim 11 wherein said first andsecond corners have a permitted difference in elevation no greater than0.001 inch.
 20. A sheet metal end closure as set forth in claim 11wherein said opening panel is of generally circular configuration andsaid deflectable portion disposed thereabout is of frusto-conicalconfiguration.
 21. A sheet metal end closure as set forth in claim 11wherein the residual stresses at the locus of separation are of suchcharacter and magnitude as to initiate fracture of the web uponlocalized interaction thereof with stresses induced by digitally appliedpressure.
 22. A sheet metal end closure as set forth in claim 11 whereinsaid opening panel is circular in shape and has a diameter in the rangeof 1/8 inch to 3/4 inch.
 23. A sheet metal end closure of at leastthree-quarter hard temper aluminum alloy of a thickness in the range of0.010 inch to 0.015 inch suitable for a pressurized fluid containercomprising a generally planar wall portion peripherally chimed forsecurement to a container body, at least one hinged inwardlydisplaceable relatively rigid circular opening panel integrally includedtherein having an inwardly domed center portion and a selectively shapedrim peripherally terminating in a particularly contoured, residuallystressed and annularly shaped fracturable web defining a locus ofseparation of said hinged opening panel from said wall portion, anintegral inclined annularly shaped deflectable portion of frusto-conicalconfiguration surrounding said opening panel and projecting outwardlyfrom the plane of said wall portion and terminating in a particularlyshaped lip integrally interconnected with the rim of said displaceableopening panel and defining therewith said fracturable web, said rim ofsaid opening panel including an upper planar surface terminallyintersecting at an angle of about 135* an angularly inclined surfacedefining the inner marginal edge of the lip of said deflectable portionin a first exposed corner, said lip of said deflectable portionincluding a planar undersurface disposed substantially coplanar with theupper surface of the rim of said opening panel and terminallyintersecting at an angle of about 135* an angularly inclined surfacedefining the outer marginal edge of the rim of said opening panel in asecond corner disposed in predetermined laterally spaced relation withsaid first corner to define, by the overlap therebetween, the lateralextent of said fracturable web, and having a permitted difference inelevation therebetween of no greater than 0.001 inch, said deflectableportion being adapted to effect, in response to digitally appliedinwardly directed pressure, a directional relative displacement of thelip thereof with the rim of said opening panel to interact with theresidual stresses extant in said web and initiate fracture thereof topermit inward displacement of a separated opening panel of greater rimsize than the size of the opening formed in said wall portion as definedby the terminal edge of the angularly inclined surface of the lip ofsaid deflectable portion, the lateral spacing of said first and secondcorners being no more than 0.004 inches and defining a web of at least apredetermined minimal extent sufficient to maintain its structuralintegrity during exposure to variations in the magnitude of the residualstress therein occasioned by normal container handling and usage andless than a predetermined maximum extent that would preclude saidfracture thereof in response to said digitally applied inwardly directedpressurE.
 24. A sheet metal end closure as set forth in claim 23 whereinsaid planar wall portion includes two displaceable opening panels ofcircular configuration, each surrounded by a deflectable portion ofannular configuration.